Boric acid, both technical and U.S.P. grades, is produced commercially by the reaction of borax (Na.sub.2 B.sub.4 O.sub.7.10H.sub.2 O) with sulfuric acid in an aqueous medium. The overall reaction that takes place between the borax and the sulfuric acid is represented by the following equation: EQU Na.sub.2 B.sub.4 O.sub.7.10H.sub.2 O+H.sub.2 SO.sub.4 .fwdarw.4H.sub.3 BO.sub.3 +Na.sub.2 SO.sub.4 +5H.sub.2 O
In a typical process borax and sulfuric acid (in stoichiometric proportions) and water are added to a reaction vessel and heated at elevated temperatures ranging from about 80.degree. C. to about 90.degree. C. Generally, however, temperatures in the range of from about 85.degree. C. to about 90.degree. C. are normally employed in most commercial processes. On completion of the reaction the reaction mixture is cooled to a temperature ranging from about 30.degree. C. to about 40.degree. C. in a crystallization or a series of crystallization vessels to cause the boric acid to crystallize out of and become suspended in the reaction medium. In addition to the technique of cooling the reaction mixture to crystallize the boric acid, evaporative and vacuum processes can also be employed to crystallize the boric acid. Regardless of the particular technique employed, the crystalline boric acid is then separated from the reaction medium or mother liquor by means of filtration and/or centrifugation and washed to remove residual impurities such as byproduct sodium sulfate.
Crystalline boric acid prepared by processes such as described above has been found to have a broad particle size distribution. Generally, however, said particles are of a mean particle size of about 190 to about 195 microns or less. Because of this small size, problems with subsequent purification, handling and storage are encountered which otherwise would not occur if crystalline boric acid having a mean particle size greater than about 190 to about 195 microns could be produced. Such small size also limits the end uses to which the boric acid can be applied.